Abstract
In this study, the natural isotopes of N (15N) and C (13C) were used to evaluate symbiotic N nutrition, C accumulation, and plant water-use efficiency in soybean varieties sampled from 37 farmers’ fields across the soybean-producing region of South Africa. The data revealed significant differences in all the parameters measured. Shoot dry matter ranged from 17 to 104 g plant−1, δ15N from −1.11 to +5.51‰, percent N derived from fixation from 21 to 96%, and N-fixed varied from 18 to 298 kg N ha−1. The high δ15N and low %Ndfa in some soybean genotypes were due to inhibition of N2 fixation by soil N uptake. Across the board, soybean variety PAN373 contributed the most symbiotic N (298, 242, and 217 kg N ha−1 in fields 3, 2 and 4, respectively, at Parys), followed by LS6164 (with 271 and 245 kg N ha−1 at Endcot field 1 and Devon field 2, respectively), and LS6150 (with 290 kg N ha−1 in field 1 at Parys). C concentration varied from 44 to 50% in soybean shoots, resulting in high shoot C ranging from 8 to 48 g C plant−1. The δ13C values of soybean shoots ranged from −27.3‰ to −21.1‰ in the 37 fields studied, with PAN1453 from Gransvlei field 1 and PAN737 from Parys field 4 exhibiting much greater δ13C values (−21.1‰ and −23.1‰, respectively), and hence increased water-use efficiency. The positive correlation found between N-fixed and dry matter yield (r = 0.70***), N-fixed and C content (r = 0.62***), and N-fixed and C concentration (r = 0.35*) indicates a functional relationship between N2 fixation and photosynthesis. Conventional tillage, as an agronomic tool, decreased water-use efficiency (or δ13C) in soybean plants possibly through alteration in soil structure and soil water retention. Due to a 2.6 °C higher daily maximum temperature in the North West Province than KwaZulu–Natal and Mpumalanga, soybean plants sampled from that province showed better growth, higher dry matter yield, and enhanced symbiotic performance. This argument was supported by a significantly positive correlation found between average daily maximum temperature and both dry matter yield (r = 0.39*), and N-fixed (r = 0.46**). Furthermore, the plants sampled from North West also showed much greater water-use efficiency due to a 127 and 67 mm less rainfall at that province than KwaZulu–Natal and Mpumalanga, respectively.
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Claims 20
Claim · model-written summary
Soybean shoot dry matter varied from 17 to 104 g plant−1.
Verbatim
e0“Shoot dry matter ranged from 17 to 104 g plant−1”
Claim · model-written summary
Soybean shoot δ15N ranged from −1.11 to +5.51‰.
- Taxon
- soybean
Glycine maxt0 - Outcome
- δ15Ne0
- Value
- −1.11 to +5.51‰e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“δ15N from −1.11 to +5.51‰”
t0“soybean (Glycine max L. Merrill)”
Claim · model-written summary
N derived from fixation ranged from 21 to 96%.
- Taxon
- soybeanGlycine maxt0
- Outcome
- percent N derived from fixatione0
- Value
- 21 to 96%e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“percent N derived from fixation from 21 to 96%”
t0“soybean (Glycine max L. Merrill)”
Claim · model-written summary
Fixed N ranged from 18 to 298 kg N ha−1.
- Taxon
- soybeanGlycine maxt0
- Outcome
- N-fixede0
- Value
- 18 to 298 kg N ha−1e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“N-fixed varied from 18 to 298 kg N ha−1”
t0“soybean (Glycine max L. Merrill)”
Claim · model-written summary
Some soybean genotypes had high δ15N and low fixation fraction due to soil N uptake inhibiting fixation.
- Taxon
- soybeanGlycine maxe0
- Outcome
- high δ15N and low %Ndfae0
- Qualifier
- inhibition of N2 fixation by soil N uptakee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The high δ15N and low %Ndfa in some soybean genotypes were due to inhibition of N2 fixation by soil N uptake”
Claim · model-written summary
PAN373 contributed the most symbiotic N, 298, 242 and 217 kg N ha−1 in Parys fields 3, 2 and 4.
- Taxon
- soybeanGlycine maxe0
- Material
- PAN373e0
- Outcome
- symbiotic Ne0
- Direction
- moste0
- Value
- 298, 242, and 217 kg N ha−1e0
- Setting
- Paryse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“soybean variety PAN373 contributed the most symbiotic N (298, 242, and 217 kg N ha−1 in fields 3, 2 and 4, respectively, at Parys)”
Claim · model-written summary
LS6164 fixed 271 and 245 kg N ha−1 at Endcot and Devon.
- Taxon
- soybeanGlycine maxt0
- Material
- LS6164e0
- Outcome
- N ha−1e0
- Value
- 271 and 245 kg N ha−1e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“LS6164 (with 271 and 245 kg N ha−1 at Endcot field 1 and Devon field 2, respectively)”
t0“soybean (Glycine max L. Merrill)”
Claim · model-written summary
LS6150 fixed 290 kg N ha−1 at Parys field 1.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“LS6150 (with 290 kg N ha−1 in field 1 at Parys)”
t0“soybean (Glycine max L. Merrill)”
Claim · model-written summary
Soybean shoot carbon concentration varied from 44 to 50%.
- Taxon
- soybeanGlycine maxe0
- Outcome
- C concentratione0
- Value
- 44 to 50%e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“C concentration varied from 44 to 50% in soybean shoots”
Claim · model-written summary
Soybean shoot carbon amount ranged from 8 to 48 g C plant−1.
- Taxon
- soybeanGlycine maxt0
- Outcome
- shoot Ce0
- Value
- 8 to 48 g C plant−1e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“shoot C ranging from 8 to 48 g C plant−1”
t0“soybean (Glycine max L. Merrill)”
Claim · model-written summary
Soybean shoot δ13C ranged from −27.3‰ to −21.1‰.
- Taxon
- soybeanGlycine maxe0
- Outcome
- δ13C valuese0
- Value
- −27.3‰ to −21.1‰e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The δ13C values of soybean shoots ranged from −27.3‰ to −21.1‰”
Claim · model-written summary
PAN1453 had elevated δ13C of −21.1‰ and inferred greater water-use efficiency.
- Taxon
- soybeanGlycine maxt0
- Material
- PAN1453e0
- Outcome
- δ13C valuese0
- Direction
- greatere0
- Value
- −21.1‰e0
- Setting
- Gransvlei field 1e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“PAN1453 from Gransvlei field 1 and PAN737 from Parys field 4 exhibiting much greater δ13C values (−21.1‰ and −23.1‰, respectively), and hence increased water-use efficiency”
t0“soybean (Glycine max L. Merrill)”
Claim · model-written summary
PAN737 had elevated δ13C of −23.1‰ and inferred greater water-use efficiency.
- Taxon
- soybeanGlycine maxt0
- Material
- PAN737e0
- Outcome
- δ13C valuese0
- Direction
- greatere0
- Value
- −23.1‰e0
- Setting
- Parys field 4e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“PAN1453 from Gransvlei field 1 and PAN737 from Parys field 4 exhibiting much greater δ13C values (−21.1‰ and −23.1‰, respectively), and hence increased water-use efficiency”
t0“soybean (Glycine max L. Merrill)”
Claim · model-written summary
N fixed correlated positively with dry matter yield (r = 0.70***).
- Taxon
- soybeanGlycine maxt0
- Outcome
- dry matter yielde0
- Direction
- positivee1
- Value
- r = 0.70***e0
- Comparator
- N-fixede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“N-fixed and dry matter yield (r = 0.70***)”
e1“The positive correlation found between N-fixed and dry matter yield”
t0“soybean (Glycine max L. Merrill)”
Claim · model-written summary
N fixed correlated positively with C content (r = 0.62***).
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“N-fixed and C content (r = 0.62***)”
e1“The positive correlation found between N-fixed and dry matter yield”
t0“soybean (Glycine max L. Merrill)”
Claim · model-written summary
N fixed correlated positively with C concentration (r = 0.35*).
- Taxon
- soybeanGlycine maxt0
- Outcome
- C concentratione0
- Direction
- positivee1
- Value
- r = 0.35*e0
- Comparator
- N-fixede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“N-fixed and C concentration (r = 0.35*)”
e1“The positive correlation found between N-fixed and dry matter yield”
t0“soybean (Glycine max L. Merrill)”
Claim · model-written summary
Conventional tillage decreased soybean water-use efficiency.
- Taxon
- soybeanGlycine maxe0
- Treatment
- Conventional tillagee0
- Outcome
- water-use efficiencye0
- Direction
- decreasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Conventional tillage, as an agronomic tool, decreased water-use efficiency (or δ13C) in soybean plants”
Claim · model-written summary
North West soybean plants had better growth, higher dry matter yield and enhanced symbiotic performance than those in the other provinces.
- Taxon
- soybeanGlycine maxe0
- Outcome
- better growth, higher dry matter yield, and enhanced symbiotic performancee0
- Comparator
- KwaZulu–Natal and Mpumalangae0
- Setting
- North West Provincee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Due to a 2.6 °C higher daily maximum temperature in the North West Province than KwaZulu–Natal and Mpumalanga, soybean plants sampled from that province showed better growth, higher dry matter yield, and enhanced symbiotic performance”
Claim · model-written summary
Daily maximum temperature correlated positively with dry matter yield (r = 0.39*).
- Taxon
- soybeanGlycine maxt0
- Outcome
- dry matter yielde0
- Direction
- positivee0
- Value
- r = 0.39*e0
- Setting
- average daily maximum temperaturee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“positive correlation found between average daily maximum temperature and both dry matter yield (r = 0.39*)”
t0“soybean (Glycine max L. Merrill)”
Claim · model-written summary
Daily maximum temperature correlated positively with fixed N (r = 0.46**).
- Taxon
- soybeanGlycine maxt0
- Outcome
- N-fixede0
- Direction
- positivee0
- Value
- r = 0.46**e0
- Setting
- average daily maximum temperaturee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“positive correlation found between average daily maximum temperature and both dry matter yield (r = 0.39*), and N-fixed (r = 0.46**)”
t0“soybean (Glycine max L. Merrill)”
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